Add comprehensive FastAPI backend for BlackRoad OS

This commit adds a complete backend infrastructure with:

**Core Infrastructure:**
- FastAPI application with async/await support
- PostgreSQL database with SQLAlchemy ORM
- Redis caching layer
- JWT authentication and authorization
- Docker and Docker Compose configuration

**API Services:**
- Authentication API (register, login, JWT tokens)
- RoadMail API (email service with folders, send/receive)
- BlackRoad Social API (posts, comments, likes, follows)
- BlackStream API (video streaming with views/likes)
- File Storage API (file explorer with upload/download)
- RoadCoin Blockchain API (mining, transactions, wallet)
- AI Chat API (conversations with AI assistant)

**Database Models:**
- User accounts with wallet integration
- Email and folder management
- Social media posts and engagement
- Video metadata and analytics
- File storage with sharing
- Blockchain blocks and transactions
- AI conversation history

**Features:**
- Complete CRUD operations for all services
- Real-time blockchain mining with proof-of-work
- Transaction validation and wallet management
- File upload with S3 integration (ready)
- Social feed with engagement metrics
- Email system with threading support
- AI chat with conversation persistence

**Documentation:**
- Comprehensive README with setup instructions
- API documentation (Swagger/ReDoc auto-generated)
- Deployment guide for multiple platforms
- Testing framework with pytest

**DevOps:**
- Docker containerization
- Docker Compose for local development
- Database migrations with Alembic
- Health check endpoints
- Makefile for common tasks

All APIs are production-ready with proper error handling,
input validation, and security measures.

backend/app/models/email.py

@@ -0,0 +1,76 @@
+"""Email models"""
+from sqlalchemy import Column, Integer, String, Text, Boolean, DateTime, ForeignKey, Enum
+from sqlalchemy.orm import relationship
+from sqlalchemy.sql import func
+import enum
+from app.database import Base
+
+
+class EmailFolderType(str, enum.Enum):
+    """Email folder types"""
+    INBOX = "inbox"
+    SENT = "sent"
+    DRAFTS = "drafts"
+    SPAM = "spam"
+    TRASH = "trash"
+    CUSTOM = "custom"
+
+
+class EmailFolder(Base):
+    """Email folder model"""
+
+    __tablename__ = "email_folders"
+
+    id = Column(Integer, primary_key=True, index=True)
+    user_id = Column(Integer, ForeignKey("users.id", ondelete="CASCADE"), nullable=False)
+    name = Column(String(100), nullable=False)
+    folder_type = Column(Enum(EmailFolderType), default=EmailFolderType.CUSTOM)
+    icon = Column(String(50))
+    created_at = Column(DateTime(timezone=True), server_default=func.now())
+
+
+class Email(Base):
+    """Email model"""
+
+    __tablename__ = "emails"
+
+    id = Column(Integer, primary_key=True, index=True)
+
+    # Sender/Receiver
+    sender_id = Column(Integer, ForeignKey("users.id", ondelete="SET NULL"))
+    sender_email = Column(String(255), nullable=False)
+    sender_name = Column(String(255))
+
+    recipient_id = Column(Integer, ForeignKey("users.id", ondelete="CASCADE"), nullable=False)
+    recipient_email = Column(String(255), nullable=False)
+
+    # CC/BCC
+    cc = Column(Text)  # Comma-separated emails
+    bcc = Column(Text)  # Comma-separated emails
+
+    # Email content
+    subject = Column(String(500), nullable=False)
+    body = Column(Text, nullable=False)
+    html_body = Column(Text)
+
+    # Metadata
+    folder_id = Column(Integer, ForeignKey("email_folders.id", ondelete="SET NULL"))
+    is_read = Column(Boolean, default=False)
+    is_starred = Column(Boolean, default=False)
+    is_draft = Column(Boolean, default=False)
+    is_spam = Column(Boolean, default=False)
+
+    # Attachments (stored as JSON array of file IDs)
+    attachment_ids = Column(Text)
+
+    # Thread
+    thread_id = Column(String(255), index=True)
+    in_reply_to = Column(Integer, ForeignKey("emails.id", ondelete="SET NULL"))
+
+    # Timestamps
+    created_at = Column(DateTime(timezone=True), server_default=func.now())
+    sent_at = Column(DateTime(timezone=True))
+    read_at = Column(DateTime(timezone=True))
+
+    def __repr__(self):
+        return f"<Email {self.id}: {self.subject}>"